1. Field of the Invention
The present invention relates generally to a rotary boring machine. More specifically, the invention relates to a rotary boring machine which does not require attaching and detaching an output signal transmission line for a dip gauge every time of connecting and disconnecting connecting rod.
2. Description of the Related Art
In general, a dip gauge and depth gauge are provided for a rotary boring machine for continuously monitoring verticality of a boring drill and a boring depth. Among these, since the depth can be measured by an extraction amount of a wire supporting the boring drill, the depth gauge can be installed at the side of a base machine. However, the dip gauge has to be installed at the tip end of the boring drill. The dip gauge must be connected to the base machine via a signal transmission line extending through a hollow interior space of the boring drill and via a slip ring. In case, the depth of boring is deep, a plurality of connecting rods must be connected above the boring drill from time-to-time according to increasing of the boring depth. Upon connection of the connecting rod, it becomes necessary to connect the signal transmission line for permitting the dip gauge to provide the information. For this purpose, a connection structure of the signal transmission lines for the output signals of the dip gauges as illustrated in FIGS. 7(a) and 7(b) are typically employed.
As shown in FIGS. 7 (a) and 7(b), a convex joint portion 1b is formed at the upper end of a hollow connection rod 1. Also, a concave joint portion 1a is formed at the lower end of the connection rod 1. A clearance d for injecting mortar is defined along the longitudinal axis of the connecting rod 1. A sheathing pipe 2 is fixedly arranged substantially along the longitudinal axis of the connecting rod 1. A concave joint 2b is provided at the upper end of the sheathing pipe 2. A conforming convex joint 2a is formed at the lower end of the sheathing pipe 2. A curled expansible code 3 forming the signal transmission line for the dip gauge is arranged through the interior space of the sheathing pipe 2. At upper and lower ends of the curled code 3, male and female connectors 4a and 4b are provided for electrical connection.
In such conventional connection structure for the signal transmission line of the dip gauge, when the connection rods are mutually connected, a worker should extract the curled code 3 from the sheathing pipe 2, and then the male and female connectors 4a and 4b are coupled or connected to each other. Thereafter, the connecting rods 1 are connected through the join portions 1a and 1b. By this, the sheathing pipes 2 of respective connecting rods 1 can be mutually connected at the joints 2a and 2b to complete connection of the connecting rods 1 with connection of the curled codes 3. Thus, the connection rods 1 are engaged in integral fashion with the engagement between the convex joint 2a and the concave joint 2b.
However, in such construction as set forth above, connection and disconnection of the connectors 4a and 4b of the curled codes 3 has to be done in a position where the connection rods 1 are positioned close proximity to one another. Placement of the connection rods 1 in the close proximity and connection and disconnection of the connectors 4a and 4b for connecting and disconnecting the curled codes 3 are substantially time-consuming and complicated work. It is also difficult to assure security for such operation. Also, due to possibility of breakage of the curled code 3 during operation, penetration of a cementing solution penetrates into the joint of the sheathing pipes 2, or wearing of shield of the curled codes 3, the curled codes 3 and the connectors 4a and 4b have to be replaced frequently. This clearly results in high cost for maintenance.